The overall aim of this project is to investigate the function of neuropeptides at synapses in the dorsal horn of the spinal cord involved in the processing of noxious peripheral stimuli. The physiology and morphological features of dorsal horn neurons have been extensively studied although the identity of transmitters released from the central terminals of cutaneous and muscle sensory afferents is still uncertain. The peptides substance P. somatostatin and cholecystokinin are contained within, and released from small diameter nociceptive sensory neurons while the opioid peptide, enkephalin is present in dorsal horn interneurons located near the terminals of nociceptive afferents. Opiates applied directly to the spinal cord produce analgesia, possibly by inhibiting the release of peptides from primary sensory terminals. To clarify the role of neuronal peptides at sensory synapses, the early development and physiology of synapses formed between identified peptide-containing sensory neurons and their target cells in the dorsel horn will be studied in dissociated cell culture. Techniques have been developed to microdissect dorsal horn neurons from embryonic rat spinal cord and to maintain these neurons in low density culture. Dorsal root ganglion neurons obtained from embryonic or neonatal rats will then be added to established cultures of dorsal horn neurons. Studies with this system will be directed as follows: 1. to record intracellularly from dorsal horn neurons and identify dorsal root ganglion neurons representing the presynaptic input to individual dorsal horn cells. 2. to examine the actions of substance P, somatostatin and cholecystokinin on dorsal horn neurons and to compare the physiological effects of peptide application with stimulation of sensory inputs to the cell. 3. to analyse the actions of opioids and other peptides on synaptic transmission between sensory and dorsal horn neurons. 4. to use immunocytochemical techniques to identify peptides within single sensory and dorsal horn neurons. 5. to use a variety of peptide and non-peptide ligands to study the appearance and distribution of peptide receptors on neurons during and after synapse formation.